Update Rust template to use ABI to connect frontend with contract

[austinabell]

This likely won't be super straightforward since the frontend code would have to be modified to conditionally use the ABI if Rust or not.

Dependent on https://github.com/near/near-abi-client-js/issues/8, and probably best to do it after an example has been ported over (to make the pattern clear).

cc @itegulov @miraclx